1. Field of the Invention
This invention generally relates to diamond-bonded materials and, more specifically, to polycrystalline diamond materials and compacts formed therefrom that are specially engineered to provide improved properties of thermal stability and mechanical strength when compared to conventional polycrystalline diamond materials.
2. Background of the Invention
Polycrystalline diamond (PCD) materials and PCD elements formed therefrom are well known in the art. Conventional PCD is formed by combining diamond grains with a suitable solvent catalyst material to form a mixture. The mixture is subjected to processing conditions of extremely high pressure/high temperature, where the solvent catalyst material promotes desired intercrystalline diamond-to-diamond bonding between the grains, thereby forming a PCD structure. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired.
Solvent catalyst materials that are typically used for forming conventional PCD include metals from Group VIII of the Periodic table, with cobalt (Co) being the most common. Conventional PCD can comprise from 85 to 95% by volume diamond and a remaining amount of the solvent catalyst material. The solvent catalyst material is present in the microstructure of the PCD material within interstices that exist between the bonded together diamond grains.
A problem known to exist with such conventional PCD materials is thermal degradation due to differential thermal expansion characteristics between the interstitial solvent catalyst material and the intercrystalline bonded diamond. Such differential thermal expansion is known to occur at temperatures of about 400° C., causing ruptures to occur in the diamond-to-diamond bonding, and resulting in the formation of cracks and chips in the PCD structure. Another problem known to exist with conventional PCD materials is also related to the presence of the solvent catalyst material in the interstitial regions and the adherence of the solvent catalyst to the diamond crystals to cause another form of thermal degradation. Specifically, the solvent catalyst material is known to cause an undesired catalyzed phase transformation in diamond (converting it to carbon monoxide, carbon dioxide, or graphite) with increasing temperature, thereby limiting practical use of the PCD material to about 750° C.
Attempts at addressing such unwanted forms of thermal degradation in PCD are known in the art. Generally, these attempts have involved the formation of a PCD body having an improved degree of thermal stability when compared to the conventional PCD material discussed above. One known technique of producing a thermally stable PCD body involves at least a two-stage process of first forming a conventional sintered PCD body, by combining diamond grains and a cobalt solvent catalyst material and subjecting the same to high pressure/high temperature process, and then removing the solvent catalyst material therefrom.
This method, which is fairly time consuming, produces a resulting diamond-bonded body that is substantially free of the solvent catalyst material, and is therefore promoted as providing a diamond-bonded body having improved thermal stability when compared to conventional PCD. However, the resulting thermally stable diamond-bonded body typically does not include a metallic substrate attached thereto, by solvent catalyst infiltration from such substrate due to the solvent catalyst removal process, as all of the solvent catalyst material has been removed therefrom.
The resulting diamond-bonded body, rendered free of the solvent catalyst material, has a coefficient of thermal expansion that is sufficiently different from that of conventional substrate materials (such as WC—Co and the like) typically infiltrated or otherwise attached to conventional PCD bodies to provide a diamond-bonded compact to adopt the diamond-bonded body construction for use with desirable wear and/or cutting end use devices. This difference in thermal expansion between the now thermally stable diamond-bonded body and the substrate, combined with the poor wettability of the diamond-bonded body surface due to the removal of the solvent catalyst material, makes it very difficult to form an adequate attachment between the diamond-bonded body and conventionally used substrates, thereby requiring that the diamond-bonded body itself be attached or mounted directly to the wear and/or cutting device.
However, since such thermally stable diamond-bonded body is devoid of a metallic substrate, it cannot (e.g., when configured for use as a cutting element in a bit used for subterranean drilling) be attached to such drill bit by conventional brazing process. Thus, use of such thermally stable diamond-bonded body in this particular application necessitates that the diamond-bonded body itself be attached to the drill bit by mechanical or interference fit during manufacturing of the drill bit, which is labor intensive, time consuming, and which does not provide a most secure method of attachment.
Additionally, because such conventional thermally stable diamond-bonded body no longer includes the solvent catalyst material, which provides properties of toughness and fracture strength, it is known to be relatively brittle and have poor impact strength, thereby limiting its use to less extreme or severe applications. This feature makes such conventional thermally stable diamond-bonded bodies generally unsuited for use in aggressive cutting and/or wear applications, such as use as a cutting element of a subterranean drilling and the like.
It is, therefore, desired that a diamond-bonded material be developed that has improved thermal stability when compared to conventional PCD materials. It is also desired that such diamond-bonded material be engineered to include a suitable substrate to form a compact construction that can be attached to a desired wear and/or cutting device by conventional method such as welding or brazing and the like. It is further desired that such thermally stable diamond-bonded material have improved properties of strength and toughness when compared to the above-noted conventional thermally stable diamond-bonded bodies. It is further desired that such diamond-bonded material and compacts formed therefrom be manufactured at reasonable cost without requiring excessive manufacturing times and without the use of exotic materials or techniques.